Q: I’m considering buying a 2003 Socata Trinidad TB20 that has an extremely low time of just over 200 hours. A single owner purchased it new and obviously hasn’t flown it much.
It has a 250-hp Lycoming IO-540 engine. The cylinder heads were nickel coated in 2017 after an inspection found pitting on the original steel cylinders, no doubt because it sat for some time between flights. The plane has never missed an annual inspection, so it must have been run at least once a year.
Since the cylinder coating in 2017, the plane still hasn’t been flown much, but I’m told that it never sits for more than a month without being run by an airplane mechanic for some period of time as it is hangared in a place that has a service center.
What are the risks with this low time, but older infrequently used engine?
A: Terry, I’m going to be very honest with you and state right out of the box that I’d be very cautious about buying this aircraft.
I think you already share the same concern that I do, and that’s the fact that this aircraft has a noted history of extended periods of inoperation.
Even though the cylinders were “nickel coated” in 2017, that doesn’t give me any additional confidence that the internal components of the engine aren’t suffering from some serious corrosion.
My greatest concern is the condition of the camshaft and tappets. Since there is no pressure oil in that area and they are lubricated by splash oil only, during extended periods of inactivity, the oil that remained on the face of the tappet bodies and the cam lobes runs off, leaving the acidic properties in the oil on those surfaces, which eventually lead to corrosion. As time passes this condition can continue to worsen.
When the engine is next started, the first pass of the cam lobe over the tappet face may begin to cause metal displacement or spalling on the cam lobe and or tappet body. Once this begins, it will never self heal, but continue to spall both surfaces. If you do an oil and filter change, you’re going to see some metal contamination in the oil filter element and things usually go down hill from there.
You mentioned that this engine seldom sits more than a month without being ground run by a mechanic and this really made my hair stand on end!
Ground running an engine is probably one of the most detrimental things you can do. That’s because the temperature does not get hot enough to boil off the condensation in the oil. The only way to boil off the condensation is to fly for at least a half hour to an hour to get the oil temperature up to at least 180° F.
If I were to consider purchasing this aircraft I would want to do the following:
I’d remove the number one and number 4 cylinders. This would give you a good chance to inspect the camshaft and tappet bodies for any indication of corrosion.
You could even go so far as to remove the number 5 cylinder as well, which would allow you to inspect the entire length of the camshaft and tappets.
Of course, there is always the possibility that just removing one cylinder will give you the information you’re looking for.
As you can imagine, an in-depth inspection like this would be a considerable expense, but if it reveals severe corrosion, you’ll know not to buy this aircraft.
The only way I would consider buying this aircraft would be to negotiate a price that would allow you to have the engine overhauled or replaced with a Factory New or Rebuilt engine. For more information regarding Lycoming’s exchange engine core policy, I’d suggest you read Lycoming Service Letter 250. You may also want to contact a Lycoming distributor who would be able to discuss your options.
Your engine would only be acceptable on an exchange basis for a Factory New or Factory Rebuilt engine because of its known history of extended periods of inactivity.
Since I’ve probably already ruined your enthusiasm about buying this aircraft, let me throw out a dollar figure for a Factory Rebuilt engine. At today’s prices you’re looking at somewhere around $46,000 in exchange for your engine.